Uses of dielectric heating/drying systems are known and are currently in use or have been proposed for use in agriculture, polymer manufacture, pharmaceuticals, bulk powder, food processing, wood products and other industries. One of the key industries using these dielectric heating/drying systems is the wood products industry and the present invention will be described particularly with respect to the wood products industry, although the invention, with suitable modifications where required, may be applied in the other industries in which dielectric heating/drying is to be performed.
In dielectric drying or heating systems particularly those used for drying wood, it is the conventional practice to load the material to be dried onto a wheeled cart and to roll the loaded cart into the kiln which is provided with rails to receive the wheels of the cart. See for example, U.S. Pat. No. 3,986,268 issued Oct. 19, 1976 to Koppelman and U.S. Pat. No. 4,472,618 issued Sep. 18, 1984 to Cloer. In these systems, the carts serve as both a conveyor and electrode. Clearly the cart which is the electrode is moveable and thus the cart-electrode must be moved into the kiln and connected electrically before the kiln chamber is closed and the drying process proceeds.
The combination of dielectric heating and the maintenance of sub-atmospheric pressure within the kiln permits extremely short drying times for lumber and other products and generally has high energy efficiency and can produce excellent dried product quality. These short drying cycles necessitate more frequent kiln loading and unloading. Cart-type handling systems in dielectric drying kilns such as that disclosed by Koppelman, though adequate, do not lend themselves to more rapid loading and unloading nor does it facilitate automatic handling or operation of the kiln.
As above indicated, all of these cart systems require manually connecting the grounding system to the cart loaded with material to be dried and positioned in the kiln before the drying cycle may be started and disconnecting the grounding system after drying and before the loaded cart may be moved from the kiln. This loading and unloading, connecting and disconnecting etc., necessitates the use of professionally trained personnel both for safety and operating procedures to better ensure there are no major problems or accidents. These limitations imposed primarily by the use of carts have given the process of dielectric drying a reputation as being non-robust in that it requires flimsy attachments which lead those in the lumber industry to imply that the technique is still in the research or experimental stage and has not yet been developed for commercial industrial purposes.
U.S. Pat. No. 3,986,268 issued Oct. 19, 1976 to Koppelman recognized the problem of carts and in one embodiment employs vertical electrodes and uses a conveyor (roller conveyor) to deliver the load to be dried into position between the vertical electrodes and then after drying to convey the dried load from between the electrodes. This system could permit computer-controlled operation, however it was found that uniform contact of the vertical electrodes with the sides of the load was difficult and could not consistently made whereby the effectiveness of the system was compromised.